1. Field of the Invention
This invention relates to frequency sources and more particularly to phase locked frequency sources which supply very high frequencies and high power levels.
2. Description of the Prior Art
It is often desirable to provide a frequency source which does not change frequency so as to drive apparatus such as transmitters at fixed frequencies. Crystal oscillators have been employed for such purposes but when the output frequency is very high, the cost of a crystal oscillator having that frequency is also very high. Voltage controlled oscillators (VCO) in a phase locked loop using a lower frequency crystal oscillator can be used to supply a very stable high frequency source but when the output power is large, it has been found that output signal may be coupled back (by radiation and/or by conduction) to the VCO and cause a phase shift that pulls the output frequency off the desired value.